Integrated circuits fabricated with bipolar technology may comprise a PNP transistor coupled to a +5.0 volts supply for providing an output signal referenced to ground. However, for special purpose circuits such as video digital-to-analog converters driving high resolution monitors, monolithic fabrication technology has generally not provided an adequately fast PNP transistor; therefore, these DACs typically comprise NPN output current sinks coupled to a resistor referenced to the positive supply. In order to interface properly with specific systems, such as a video monitor, it is desired to place the positive supply at ground potential. If the input signals are standard ECL, then a single supply circuit will suffice. However, where TTL inputs or above ground ECL inputs are encountered, having the positive supply at ground will be less than desirable.
The variety of supply options and logic thresholds could be covered by a variety of devices, each one fitting a particular application. However, it would be more desirable to have as many options as practical in a single device.
Thus, what is needed is a translation circuit that selectably operates on either a single supply voltage or dual supply voltages for providing an output signal referenced to a specific voltage regardless of an input signal voltage reference.